Optimizing Ionic Transport through a Bilayer Nanoporous Graphene by Tuning the Direction of Electric Fields

Nanoporous graphene (NPG) serves as an excellent platform for ionic transport, enabling wide applications, from desalination to energy harvesting. However, the misalignment of pores in multilayer graphene will obviously impede ionic transport, which is unconducive to practical applications. With the hope of improving ionic transport through misaligned NPGs, in this work, a series of molecular dynamics simulations are employed to investigate ion and water transport across a bilayer NPG with different pore offset distances and functionalization, particularly focusing on the electric field direction. Under the drive of an increased axial electric field, the counterion flux shows nearly linear trends for small offsets, leading to unidirectional water transport. Increasing offsets can significantly weaken the competitive transport of cations and anions, resulting in a higher degree of unidirectional water transport. By tuning the direction of the electric field, the counterion flux exhibits interesting maximum behaviors at a critical angle between the external field and the nanopore axis, accordingly promoting the net water flux in NPGs with large offsets dramatically. The potential of mean force (PMF) barriers can intuitively decipher the enhancement in counterion and water fluxes. Additionally, the dynamics of water and ions also exhibit bifurcations for cationic and anionic pore functionalization. Our results offer a new approach to promote the transport of water and ions in misaligned NPGs and provide practical insights into the design of novel nanometer water pumps.